The present invention relates to a method of producing a nozzle for a solenoid valve, and more specifically the preestimation relates to a method of producing a cylindrical nozzle including a bottom having a seat is provided for receiving a valve body.
A solenoid valve is used in many fields for example as a fuel injection valve and oil pressure control valve. Before explaining a conventional production method of a nozzle incorporated with the solenoid valve, a structure of the solenoid valve is illustrated in FIG. 5.
As illustrated in FIG. 5, a solenoid type fuel injection valve feeds fuel into an automobile engine, in which a main body 10 of the fuel injection valve feeds a solenoid coil 11, a yoke 12 for accommodating a core 13 and a nozzle 1 mounted on the lower part of the yoke 12.
At the lower center portion of the yoke 12, is a flow passage aperture 12a is formed which includes a part of a fuel passage. A plunger 14 including a ball type valve body 15 fits into the flow passage aperture 12a while permitting axial reciprocating movement via return spring 17 biasing the valve body 15 to contact a seat portion is provided at the nozzle 1 when the solenoid coil 11 is not energized.
The nozzle 1 is in a shape of cylinder with a bottom, and at the center on the upper face of the bottom, the seat portion 1a of an inverted conical shape and a fuel injection hole 9 are provided. Further, above the upper face of the bottom, a swirler 16 is disposed to guide the reciprocating motion of the valve body 15 and to swirl the fuel.
When the solenoid coil 11 is energized, the plunger 14 includes a magnetic circuit together with the yoke 12 and core 13 and moves via magnetic attraction against the biasing force of the return spring 17 by a predetermined stroke. By this attracting operation, the valve body 15 moves away from the seat portion 1a and opens the valve. Thus, the fuel is swirled and atomized via the swirler 16 and is injected from the fuel injection hole 9.
In such fuel injection valve, the sealing the property between the seat portion 1a and the valve 15 is an important parameter during the valve closing period. Specifically, during the non-energizing period of the solenoid coil 11. An accurate roundness and an accurate surface roughness are required for the seat portion 1a to achieve an accurate seat between seat portion 1a and valve body 15. Generally, a roundness less than 1 .mu.m and a surface roughness of Rmax 1.0 are necessary for the seat portion 1a of the fuel injection valve.
Now, a conventional method of producing the nozzle of the fuel injection valve, in particular method of forming the seat portion of the nozzle is explained.
The valve body and the seat portion used for a fuel injection valve are subject to frequent opening and closing operations; thus, material having excellent abrasion resistance and corrosion resistance to the fuel are required. Typically, martensite series stainless steel is used as a nozzle blank. However, martensite series stainless steel is known to be a material which is difficult to accurately apply plastic working, therefore in a conventional nozzle production, thereafter a worked blank is hardened and finally the seat portion is polished to finish the seat portion.
Further, for to improve oil tightness, which is a sealing property of the nozzle seat portion a method of polishing is known by placing a lapping material or abrasive grain between the seat portion and the valve body and thereafter rotating one of the seat portion and the valve body to obtain a fit, and by applying burnishing work to the seat portion as disclosed in JP-A-60-119369(1985) which corresponds to U.S. Pat. No. 4,651,926.
As is understood from the above explanation, the conventional nozzle product method necessitates the processes of cutting and polishing the nozzle seat portion which require a longer time than a plastic working.
In particular, with respect to the finishing work of the nozzle seat portion by polishing after the hardening thereof which was carried out for maintaining the oil tightness and dimensional accuracy in the conventional production method, a strict control of the wear of the abrasive is required for maintaining the dimensional accuracy of the seat portion, and further, the working machine must be maintained a state of a high accuracy because of the relatively small diameter of the seat portion. This small diameter requires that work jigs of the working machine operate at a rotational high speed and a high dimensional accuracy. Practicing this method reduces the productivity of the nozzle and increases the production cost.
In the method where lapping material is disposed between the seat portion and the valve body, and either the seat portion or the valve body to obtain a fit is rotated, it takes a long time to complete the fitting work such that problems of low productivity result from this method.
In the method where burnishing work is applied to the seat portion, the burnishing work includes rotating a burnishing jig. As a result the burnishing jig is likely seize the portion to be worked. For preventing such seizure, a jig with a lubricant oil groove is used; however, a problem arises such that an dimensional accuracy of the nozzle seat portion is insufficient because the construction of the jig deviates from the required construction for the nozzle seat portion.